Plasma processing apparatus and plasma processing method

ABSTRACT

A plasma processing apparatus including a processing state detection unit having: a light emission detection unit to detect light emission of the plasma; a calculation unit to obtain a differential waveform data of the light emission of the plasma; a database unit that stores a plurality of pieces of differential waveform pattern data in advance; a film thickness calculation unit to calculate an estimated value of the film thickness of the processing target film processed on the processing target material by weighting based on differences between the differential waveform data obtained by the calculation unit and the plurality of pieces of differential waveform pattern data stored in the database unit; and an end point determination unit to determine an end point of processing using the plasma based on the estimated value of the film thickness of the processing target film calculated by the film thickness calculation unit.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a processing apparatus and a processingmethod for a processing target material in manufacture of asemiconductor integrated circuit and the like, and particularly relatesto a plasma processing apparatus and a plasma processing method suitablefor accurately detecting etching amounts of various layers provided on asubstrate by etching processing using plasma discharge and processing toa desired film thickness and etching depth.

2. Description of the Related Art

In manufacture of a semiconductor device, a process using a dry etchingapparatus is widely used for removal or pattern formation of layers ofvarious materials and particularly layers of dielectric materials formedon a surface of a semiconductor wafer.

In the dry etching apparatus, processing gas introduced into a vacuumprocessing chamber is converted into plasma containing ions andradicals, and the ions and radicals are reacted with the layers formedon the surface of the semiconductor wafer, thereby performing an etchingprocess of the semiconductor wafer.

What is important in the etching process is to accurately detect anetching end point for stopping the etching process at the desired filmthickness and etching depth during the processing of such a layer.

During dry etching processing of the semiconductor wafer, an emissionintensity of a specific wavelength in plasma light changes as etching ofa specific film progresses. Therefore, as one method for determining theetching end point of the semiconductor wafer, in related arts, there isa method in which in a dry etching processing, a change in an emissionintensity of a specific wavelength from plasma is detected, and anetching end point of a specific film is detected based on the detectionresult.

As an example of such a technique in the related arts, a techniquedescribed in JP-A-2007-234666 (PTL 1) has been known. In the techniquein the related art, a method of performing end point determination basedon a time change of an amount of reflected light from a semiconductorwafer during etching is described.

Since the amount of the reflected light from the semiconductor waferchanges depending on film thicknesses of layers other than a layer beingprocessed, JP-A-2016-184638 (PTL 2) has been known in the related artsas a method for accurately detecting an end point under such acondition. In the technique in the related arts, a highly accurate filmthickness estimation method when a film thickness of a layer under aprocessing target film (base film thickness) is different is disclosed.

PTL 1 discloses a method of obtaining a characteristic behavior of timechange of interference light by detection, creating a database based onthe behavior, and determining the end of etching by comparing thedatabase and a detected interference waveform. The database is createdby setting a standard pattern showing a wavelength dependence of theinterference light with respect to an etching amount of a processingtarget material such as a semiconductor wafer that is used for samples(semiconductor wafer used for samples) when plasma etching theprocessing target material.

PTL 2 describes preparing interference spectrum patterns (interferencepatterns) with different base film thicknesses as databases, creating adatabase generated by synthesizing two databases, comparing thesynthesized database and a detected interference pattern, calculating anestimated film thickness value at each time point, and determining theend point.

However, in the above-described related arts, in addition to the basefilm thickness, a mask film thickness varies, a mask width varies, andthe film thickness varies depending on a position on the semiconductorwafer of the processing target film, and when various variations such asthe above ones occur in a fine shape of a semiconductor wafer surface,highly accurate film thickness estimation cannot be achieved.

For example, consider a case where the base film thickness and the maskfilm thickness are different, and the fine shape of the semiconductorwafer to be processed has a slightly thick base film thickness or aslightly thick mask film thickness. In this case, it is necessary toprepare a database of interference spectrum patterns obtained from foursemiconductor wafers whose base film thickness is thick or thin andwhose the mask film thickness is thick or thin, and to synthesize theabove appropriately, whereas neither PTL 1 nor PTL 2 discloses such amethod.

In consideration of the above-mentioned problems of the related arts, anobject of the present invention is to provide a plasma processingapparatus and a plasma processing method that can accurately detect orcontrol the remaining film thickness of the processing target film evenwhen two or more variations occur in the fine shape of the semiconductorwafer surface (for example, the base film thickness and the mask filmthickness).

SUMMARY OF THE INVENTION

In order to achieve the above object, a plasma processing apparatusaccording to the invention includes: a vacuum processing chamberconfigured to generate plasma in a state where an inside of the vacuumprocessing chamber is exhausted to vacuum, so as to process a processingtarget material; a processing state detection unit configured to detecta state of a processing target film of the processing target materialwhich is processed inside the vacuum processing chamber; and a controlunit configured to control the vacuum processing chamber and theprocessing state detection unit. The processing state detection unitincludes: a light emission detection unit configured to detect lightemission of the plasma generated inside the vacuum processing chamber; acalculation unit configured to obtain a differential waveform data ofthe light emission of the plasma detected by the light emissiondetection unit; a database unit that stores a plurality of pieces ofdifferential waveform pattern data in advance; a film thicknesscalculation unit configured to calculate an estimated value of the filmthickness of the processing target film processed on the processingtarget material by weighting based on differences between thedifferential waveform data obtained by the calculation unit and theplurality of pieces of differential waveform pattern data stored in thedatabase unit; and an endpoint determination unit configured todetermine an end point of processing using the plasma based on theestimated value of the film thickness of the processing target filmcalculated by the film thickness calculation unit.

In order to achieve the above object, a plasma processing method using aplasma processing apparatus in which plasma is generated and aprocessing target film formed on a processing target material isprocessed in a state where an inside of a vacuum processing chamber isexhausted to vacuum, including: a step of detecting, by a light emissiondetection unit at a time instance during a period of processing theprocessing target film, light emission of the plasma generated insidethe vacuum processing chamber; a step of obtaining, by a calculationunit, a differential waveform data of a plurality of wavelengths of thelight emission of the plasma detected by the light emission detectionunit; a step of calculating, by a film thickness calculation unit, anestimated value of the film thickness of the processing target filmprocessed on the processing target material at said time instance byweighting each thickness value of the processing target film which isindicated by each corresponding pattern in the plurality of differentialwaveform pattern data stored in a database unit in advance based on adifference between the differential waveform data obtained in the timeinstance by the calculation unit and each value of the plurality ofdifferential waveform pattern data; and a step of determining, by an endpoint determination unit, an end point of processing using the plasmabased on the estimated value of the film thickness of the processingtarget film calculated by the film thickness calculation unit.

According to the invention, even when various variations occur in thefine shape of the semiconductor wafer, a processing amount or aremaining film thickness of the processing target film can be detectedwith high accuracy.

According to the invention, highly accurate film thickness estimationand end point determination under various structural variations betweenwafers, lots, and the like can be achieved, and a yield of devicemanufacturing can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a schematic configuration of a plasmaprocessing apparatus according to an embodiment of the invention.

FIG. 2A is a cross-sectional view of a processing target materialaccording to the embodiment of the invention, showing a state beforeprocessing.

FIG. 2B is a cross-sectional view of the processing target materialaccording to the embodiment of the invention, showing a state during theprocessing.

FIG. 3A is an explanatory diagram of matrix data used in calculationaccording to the embodiment of the invention.

FIG. 3B is an explanatory diagram of the matrix data used in thecalculation according to the embodiment of the invention.

FIG. 4 is a graph showing a differential waveform pattern used in thecalculation according to the embodiment of the invention.

FIG. 5A is a graph showing variations in a differential waveform patternextracted from a database used in the calculation according to theembodiment of the invention.

FIG. 5B is a graph showing a standard deviation obtained from thevariations in a differential waveform pattern extracted from a databaseused in the calculation according to the embodiment of the invention.

FIG. 6 is a flowchart showing a procedure for calculating a remainingfilm thickness or an etching amount of the processing target film in theetching process according to the embodiment of the invention.

FIG. 7 is a flowchart showing a detailed procedure of recipeoptimization in step S603 of the flowchart in FIG. 6.

FIG. 8 is a graph showing a differential waveform pattern obtained bydetecting reflected light from a wafer to be processed and adifferential waveform pattern stored in the database that explains aneffect of the etching process according to the embodiment of theinvention, and shows that the film thickness can be detected with highaccuracy by using differential waveform pattern databases measured ontest semiconductor wafers with similar fine shapes by weighting thedifferential waveform pattern databases, even when the fine shape of theprocessing target material varies.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the invention, a plasma processing apparatus is equippedwith an etching amount measuring unit having a plurality of interferencespectra of various film thicknesses and structures in databases. Theetching amount measuring unit mixes the film thicknesses of thedatabases based on distances between an interference spectrum duringetching and the databases, and determines an estimated film thicknessvalue, and thereby film thickness estimation with high accuracy can beachieved even in a case where variations exist in film thickness andstructure other than the base film thickness.

A specific procedure for estimating the film thickness in the inventionwill be described below.

(a) Prepare a plurality of databases having different interferencespectrum patterns due to various film thicknesses and structures.

(b) Calculate weights according to differences between the interferencespectrum pattern during wafer processing and the patterns of theinterference spectra of the databases, and calculate the estimated filmthickness value by using the weights and the film thickness values ofthe databases.(c) Determine that a target is reached by using the estimated filmthickness.

Here, as for explaining the calculation of the estimated film thicknessvalue more specifically, a wavelength range of an interference spectrumis optimized by using data on interference spectrum and film thicknesscollected in advance. Specifically, a wavelength range in whichinterference spectra have a large variation in the same film thicknessis excluded, and accuracy is evaluated by mutual film thicknessestimation between databases. If the accuracy is good, the wavelengthrange is used for the film thickness estimation.

In the present invention, in the plasma processing apparatus and theplasma processing method, by using three or more interference lightpatterns for synthesis weighted in accordance with a value of adifference between an actual interference light pattern duringprocessing and the actual interference light pattern for synthesis, andsynthesizing film thicknesses respectively calculated from theinterference light patterns for synthesis according to the weights, thefilm thickness during processing can be detected.

According to the invention, considering that fine shapes onsemiconductor wafer surfaces are different, differential waveformpattern databases of the interference light obtained from a plurality ofsemiconductor wafers are registered, a time derivative for each of theplurality of wavelengths of the interference light obtained from thesemiconductor wafer surface during the etching processing is obtained, adifferential value pattern of the waveform of the interference light isobtained, and weights based on the pattern differences between thepattern and the plurality of differential waveform pattern databases arerespectively calculated for the differential waveform pattern databases.

The invention relates to a plasma processing apparatus and a plasmaprocessing method capable of detecting the remaining film thickness ofthe processing target film with high accuracy by calculating a weightedsum of film thicknesses calculated from the differential waveformpattern databases using the weights described above, by using patterndatabases whose fine shapes are more similar to that of the processingtarget semiconductor wafer.

Hereinafter, an embodiment according to the invention will be describedin detail with reference to drawings. In all the drawings for explainingthe present embodiment, those having same functions are denoted by samereference numerals, and repeated descriptions thereof will be omitted inprinciple.

However, the invention should not be construed as being limited to thedescription of the embodiment described below. Those skilled in the artcould have easily understood that specific configurations can be changedwithout departing from the spirit or scope of the invention.

First Embodiment

Hereinafter, with reference to FIGS. 1 to 5, an overall configuration ofthe plasma processing apparatus for a semiconductor wafer provided withmeans for detecting the etching amount (here, the actual etching depthand the film thickness of the processing material) according to theinvention will be described.

The plasma processing apparatus according to the embodiment of theinvention is shown in FIG. 1. The plasma processing apparatus 1 includesa vacuum processing chamber 2, an etching amount measuring unit 8, and acontrol unit 30.

The vacuum processing chamber 2 includes, on an inside thereof, a sampletable 5 on which a processing target material 4 such as a semiconductorwafer is placed, a light receiver 7 for detecting light emitted from theplasma 3 generated inside, an optical fiber 71 that transmits the lightemitted from the plasma 3 received by the light receiver 7, and a lightsource 22 that irradiates the processing target material 4 with light.The vacuum processing chamber 2 further includes a gas introducing unitfor introducing gas into the inside, a vacuum exhausting unit forexhausting the inside into vacuum, a power supply unit for supplyingelectric power, and the like (not shown for the sake of simplicity).

The etching amount measuring unit 8 includes a spectroscope 9, a firstdigital filter 10, a differentiator 11, a second digital filter 12, anindividual film thickness calculator 13, a differential waveform patterndatabase set 14, a differential waveform pattern database 15, a weightedfilm thickness calculator 16 for calculating a film thickness 210 of theprocessing target film, a film thickness calculating recipe 17 used forcalculation of the weighted film thickness calculator 16, a regressionanalyzer 18, an end point determiner 19 that determines the end ofetching based on a result of the regression analyzer 18, a display 20that displays a determination result of the end point determiner 19, anda recipe optimizer 21 that optimizes the values of the film thicknesscalculating recipe 17.

The etching amount measuring unit 8 in FIG. 1 shows a functionalconfiguration, and an actual configuration of the etching amountmeasuring unit 8 excluding the display 20 and the spectroscope 9 caninclude: a CPU; a storage device including a ROM that holds various datasuch as an etching depth and film thickness detection processing programand a differential waveform pattern database of interference light 6, aRAM for holding detection data, and an external storage device; a datainput and output device; and a communication control device.

The control unit 30 receives a signal from the etching amount measuringunit 8 and a signal from the outside, and controls the gas introducingunit, the vacuum exhausting unit, the power supply unit, and the like(not shown) connected to the vacuum processing chamber 2.

Etching gas introduced into the inside of the vacuum processing chamber2 from the gas introducing unit (not shown) is decomposed into theplasma 3 by microwave power or the like supplied from the power supplyunit (not shown), and the plasma etches the processing target material4, such as the semiconductor wafer, on the sample table 5.

The light emitted from the plasma 3 is directly received by the lightreceiver 7, or is partially received by the light receiver 7 after beingreflected by the processing target material 4 such as a semiconductorwafer, such as the interference light 6, and is introduced into thespectroscope 9 from the vacuum processing chamber 2 through the opticalfiber 71. In the spectroscope 9, the incident light emission of theplasma is separated and light intensities are converted into a digitalsignal. Instead of emitting light from the plasma 3, light may beirradiated from the light source 22 to the processing target material 4,and reflected light may be measured by the spectroscope 9.

FIG. 2A shows a fine shape of a surface of the processing targetmaterial 4, which is to be etched. The processing target material 4,such as a semiconductor wafer, is formed by laminating, for example, aprocessing target film 202 containing polysilicon or the like and a basefilm 203 including an oxide film or the like on a silicon substrate 200.A pattern of the mask 201 made of a resist or the like is formed on theprocessing target film 202.

FIG. 2B is a schematic view when the processing target film 202 is beingetched. The plasma light 204 incident on the processing target material4 is reflected on the surface of the processing target material 4, inwhich, first, reflected light 205 on the surface of the mask 201 andreflected light 206 at a boundary between the mask 201 and theprocessing target film 202 exist. Also, reflected light 207 on thesurface of the processing target film 202 in a part where the processingtarget film 202 is exposed and not covered with the mask 201, reflectedlight 208 at a boundary between the processing target film 202 and thebase film 203, and reflected light 209 at a boundary between the basefilm 203 and the silicon substrate 200 exist.

Interference light is formed because an optical path difference occursbetween the reflected lights. Since a thickness of the processing targetfilm 202 decreases as the etching progresses, the optical pathdifference of each reflected light changes, and an interferencephenomenon having a different period for each wavelength occurs. Amongthe multi-wavelength interference lights 6, multi-wavelengthinterference light 6 received by the light receiver 7 is guided to thespectroscope 9 of the etching amount measuring unit 8 via the opticalfiber 71, and based on this state, the etching amount of the processingtarget film 202 is measured and the end point determination of a process(here, etching) is performed.

In FIG. 2B, the film thickness as a film thickness to be detected is thefilm thickness 210 of the processing target film 202. However, themulti-wavelength interference light received by the light receiver 7 andmeasured by the spectroscope 9 varies depending on variations in thefine shape of the semiconductor wafer, such as variations for each ofthe mask film thickness 211, the base film thickness 212, an area ratioof processing target film area 213 to a mask area 214, and a position onthe semiconductor wafer of the film thickness 210 of the processingtarget film. The variations are main reason of errors in detecting thefilm thickness 210 of the processing target film.

The multi-wavelength interference light 6 with respect to the processingtarget material 4 taken in by the spectroscope 9 becomes currentdetection signals corresponding to the emission intensities of thewavelengths respectively, and the current detection signals areconverted into voltage signals. A plurality of signals having specificwavelengths output as sampling signals obtained by the spectroscope 9 atany sampling time point i are temporarily stored in a storage devicesuch as a RAM (not shown) as time series data yij. Here, j indicates awavelength.

Next, the time series data yij output from the spectroscope 9 andtemporarily stored in a storage device such as a RAM is transmitted tothe first digital filter 10, waveforms having a frequency higher than apredetermined frequency, which are noise components, are removed,thereby smoothing processing is performed, and smoothed time series dataYij is temporarily stored in the storage device such as a RAM (notshown).

The smoothed time series data Yij temporarily stored in the storagedevice such as a RAM is transmitted to the differentiator 11, and thetime series data dij of a differential value (first order differentialvalue or second order differential value) at a predetermined samplingtime point i is calculated and stored in the storage device such as aRAM (not shown). The time series data dij of the differential valuetemporarily stored in the storage device such as a RAM is transmitted tothe second digital filter 12, smoothing processing is performed again,and smoothed differential coefficient time series data Dij is stored inthe storage device such as a RAM (not shown).

Here, the calculation of the smoothed differential coefficient timeseries data Di will be described. A secondary Butterworth type low passfilter, for example, is used as the first digital filter 10. Smoothedtime series data Yi by the secondary Butterworth type low pass filter isobtained by Equation (1).Yi=b1·yi+b2·yi−1+b3·yi−2−[a2Yi−1+a3·Yi−2]   (Equation 1)Here, coefficients a and b have different numerical values depending ona sampling frequency and a cutoff frequency. Coefficient values of thedigital filter are, for example, a2=−1.143, a3=0.4128, b1=0.067455,b2=−0.013491, b3=0.067455 (sampling frequency is 10 Hz, and cutofffrequency is 1 Hz).

The time series data di of differential coefficient is calculated by thedifferentiator 11 from Equation (2) using a polynomial adapted smoothingdifferential method with the time series data Yi at five points asfollows.

$\begin{matrix}{{di} = {{\sum\limits_{k = {- 2}}^{k = 2}{\omega\;{k \cdot {Yi}}}} + k}} & \left( {{Equation}\mspace{14mu} 2} \right)\end{matrix}$Here, with respect to the weight coefficient ω, ω⁻²=2, ω⁻¹=−1, ω₀=−2,ω₁=−1, and ω₂=2.

The smoothed differential coefficient time series data Di by using thetime series data di of the differential coefficient is calculated asfollows from Equation (3) by, for example, a secondary Butterworth typelow pass filter as the second digital filter 12.Di=b1·di+b2·di−1+b3·di−2−[a2·Di−1+a3·Di−2]   (Equation 3)

The calculation can be performed for each wavelength j to obtainsmoothed differential coefficient time series data Dij. A value obtainedby dividing the smoothed differential coefficient time series data Dijby the smoothed time series data Yij is used as Dij in subsequentcalculations. The smoothed differential coefficient time series data Dijmay also be used as it is.

On the other hand, the differential waveform pattern database set 14holds three or more differential waveform pattern databases 15. Each ofthe differential waveform pattern databases 15, stores in advanceinterference light pattern data P(m)sj obtained when a test processingtarget material having the same material, shape, and composition as theprocessing target material 4 which is to be processed for manufacturinga semiconductor device and a film structure on a surface thereof isetched under the same condition as the processing target material 4.

The differential waveform pattern database 15 stores a plurality ofpieces of data measured in a plurality of different test processingtarget materials. m indicates an ID of a database, s indicates anelapsed time at a time of sampling counted from a start of theprocessing, and j indicates an emission wavelength. The interferencelight pattern data P(m)sj includes a pattern of intensity of theinterference light from the processing target film, which corresponds todifferent remaining film thicknesses of the processing target film or avalue of data indicating the remaining film thickness.

When the etching proceeds in a lateral direction as well, a parameterindicating a width of the processing target film area 213 or a width ofthe mask area 214 may be included instead of the remaining filmthickness. The differential waveform pattern database 15 is stored in amemory device as a RAM or ROM, or a storage device such as a hard diskor a DVD disk inside the etching amount measuring unit 8 (not shown).

The differential waveform pattern databases 15 stored in thedifferential waveform pattern database set 14 is obtained from materialsto be processed having slightly different fine shapes, such as thickerand thinner masks 201, due to manufacturing variations and the like. Thedifferential waveform pattern databases 15 may be created by preparingtest materials to be processed having slightly different fine shapes.

The individual film thickness calculator 13 is a process of extractingthe remaining film thickness of the processing target film and theinterference light pattern data P(m) sj from the above-mentioneddifferential waveform pattern databases 15. For example, for each of theabove differential waveform pattern databases 15, data in which s isequal to or longer than a predetermined elapsed time and remaining filmthickness data corresponding to the time may be extracted.

An elapsed time having the smallest pattern difference and a filmthickness value at the time may be detected by comparing each of theabove differential waveform pattern databases 15 with the actual patternDij of the interference light corresponding to the predetermined elapsedtime. That is, differences between the pattern data P(m)sj stored in thedifferential waveform pattern databases 15 and the actual pattern Dijmay be calculated, pattern data having the smallest difference value maybe obtained, and the remaining film thickness corresponding to thepattern data may be extracted.

The interference light pattern data extracted in such manner is calledQ(m)sj. The data is associated with a remaining film thickness at theelapsed time. The associated remaining film thickness is called r(m)s.

The weighted film thickness calculator 16 calculates a value of aninstantaneous film thickness value Zi at the time point i by using theinterference light pattern data Q(m)sj and the remaining film thicknessdata r (m) s extracted for each database. In order to calculate theinstantaneous film thickness value Zi, a matrix R: 301 shown in FIG. 3Aand a matrix Q: 302 shown in FIG. 3B are created here.

The matrix R: 301 in FIG. 3A is a matrix in which r(m)s are connected inan order from m=1 in a row direction. In the following, an element onthe uth row is represented by Ru. The matrix Q: 302 in FIG. 3B is amatrix in which Q(m)sj are connected in an order from m=1 in a rowdirection. In the following, an element on the uth row and the withcolumn is represented by Quv. Ru and Quv are each associated with thesame elapsed time in the same database. In the following, N is used asthe number of rows.

The value of the instantaneous film thickness value Zi is calculated bythe following Equations (4) and (5).Zi=R ^(T) ·A·W  (Equation 4)

The above is a matrix calculation formula, and A and W are the followingmatrices, respectively. T represents a transpose.

A: a matrix for correction having N rows and N columns. A may also be adiagonal matrix having N rows and N columns, in which each element is areciprocal of a sum of elements of W. Also, A may be an inverse matrixof (K−λI) like Kernel ridge regression. Here, K is a matrix having Nrows and N columns in which an element on the uth row and the withcolumn is kuv represented by the following Equation (5). λ is anarbitrary coefficient, and I is an identity matrix having N rows and Ncolumns whose elements are 1.

$\begin{matrix}{{kuv} = {\exp\left( {- \;{\sum\limits_{j}{{\left( {{Quj} - {Qvj}} \right)^{2}/2}\sigma^{2}}}} \right)}} & \left( {{Equation}\mspace{14mu} 5} \right)\end{matrix}$

In the above Equation (5), a wavelength range for summing j and acoefficient σ are specified by the values stored in the film thicknesscalculating recipe 17. exp is an exponential function with a base of thenatural logarithm.

W: each element shows a weight according to a pattern difference betweenthe smoothed differential value time series data Dij at the time point iand data in each database. For example, a value of the uth element Wu iscalculated by a function that monotonically decreases according to amagnitude of the pattern difference, as in the following Equation (6).

$\begin{matrix}{{wu} = {\exp\left( {- {\sum\limits_{j}{{\left( {{{Dij}--}{Quj}} \right)^{2}/2}\sigma^{2}}}} \right)}} & \left( {{Equation}\mspace{14mu} 6} \right)\end{matrix}$

In the above Equation (6), the wavelength range for summing j and thecoefficient σ are specified by values stored in the film thicknesscalculating recipe 17 in the same manner as in the Equation (5).

By using the above Equation (6), the differential waveform pattern ofthe processing target material 4 at the time point i and thedifferential waveform pattern of each database that are more similarhave a large value, and those that are less similar obtains a smallweight. By using such weights in the Equation (4), the instantaneousfilm thickness value Zi is calculated from the remaining film thicknessin databases having similar differential waveform patterns.

For example, as shown in FIG. 4, when a differential waveform pattern410 of the processing target material 4 and differential waveformpatterns 401 to 403 of databases are obtained, by giving large weightsto the differential waveform pattern 401 of DB1 and the differentialwaveform pattern 402 of DB2, and giving a small weight to thedifferential waveform pattern 403 of DB3, the instantaneous filmthickness value Zi is calculated from the differential waveform pattern401 of DB1 and the differential waveform pattern 402 of DB2, which arecloser to the differential waveform pattern.

If the fine shape on the surface of the processing target material 4 issimilar, the differential waveform pattern of the interference lightalso takes a similar pattern, and therefore, as a result, theinstantaneous film thickness value Zi can be calculated using a databasehaving a similar fine shape on the surface of the processing targetmaterial 4. A calculation equation of the weight Wu is not limited toEquation (6), and may be a function in which a small weight iscalculated when the pattern difference is large.

The instantaneous film thickness value at the sampling time point isdetected as Zi, and the value of the instantaneous film thickness valueZi is stored in the storage device in the etching amount measuring unit8 as time series data.

The film thickness calculating recipe 17 is data for designating awavelength range for summing in the above-mentioned equations (5) and(6) and the coefficient σ in the equations. The data may be determinedby the designer or may be set by the recipe optimizer 21 to be describedlater.

In the regression analyzer 18, at the same time when an output from theweighted film thickness calculator 16 is received or data of theinstantaneous film thickness Zi at the sampling time point i stored inthe storage device is read, an instantaneous film thickness value beforethe time point i is read from the storage device, and the output or thedata of the instantaneous film thickness Zi and the instantaneous filmthickness value are used for a regression analysis, so as to calculate afilm thickness value at the time point i from a result of regressionline approximation.

That is, a first order regression line Y=Xa·t+Xb (Y: remaining filmamount, t: etching time, Xa: an absolute value is an etching rate, Xb:initial film thickness) is obtained by the regression analyzer 18, and avalue of a film thickness Yi (calculated film thickness) at the samplingtime point is calculated from the regression line. When a desiredremaining film thickness of the processing target film is smaller thanthe remaining film thickness in the differential waveform patterndatabase 15, the film thickness value of the time point i may becalculated using only the first order regression line withoutcalculating the instantaneous film thickness Zi.

Next, the data indicating the obtained value of the calculated filmthickness Yi is transmitted to the end point determiner 19, in the endpoint determiner 19, the value of the film thickness Yi and a filmthickness value that is a target of the etching processing (target filmthickness) are compared, and when it is determined that the filmthickness Yi is equal to or smaller than the target film thicknessvalue, it is regarded that the etching amount of the film to be etchedof the processing target material 4 arrives the target, and a resultthereof is displayed on the display 20.

After that, generation of an electric field or a magnetic field of theplasma forming portion is stopped, the plasma 3 disappears, and theetching process of the processing target material 4 is completed, andthen the processing conditions such as gas and pressure for the etchingprocessing are changed to process the film to be etched.

The recipe optimizer 21 performs a processing of setting theabove-described film thickness calculating recipe 17. This is performedas a pre-processing before plasma processing of the processing targetmaterial 4 starts. The recipe optimizer 21 extracts a differentialwaveform pattern at a specified remaining film thickness (for example,target film thickness) from each database among the differentialwaveform pattern databases 15. Extracted differential waveform pattern501 of the DB1, differential waveform pattern 502 of the DB2, anddifferential waveform pattern 503 of the DB3 are shown in FIG. 5A.

A standard deviation 510, which is a variation in intensity at eachwavelength of the extracted differential waveform pattern, is calculatedas shown in FIG. 5B. Since it is assumed that the intensity variesdepending on factors other than the remaining film thickness, such asstates of the plasma or the chamber, the accuracy can be improved byexcluding the wavelength with a large variation.

Therefore, in FIG. 5B, the wavelength range is stored in the filmthickness calculation recipe 17 such that the instantaneous filmthickness Zi is calculated using only the wavelength range of 512, whileexcluding wavelengths having a large standard deviation as shown in 511from wavelengths for summing in Equations (4) and (5).

The wavelength range to be excluded may be determined in relativemagnitude such as the wavelength of top 10% or 20% of the variationamong all wavelengths, or a threshold value may be set for thevariation. When a differential waveform pattern of a database is dividedinto a plurality of groups, standard deviations for the groups may becalculated respectively, and an average thereof may be used.

To determine a percentage of wavelength ranges to be excluded, therecipe optimizer 21 extracts one database (DBp) among the differentialwaveform pattern databases 15 and calculates the instantaneous filmthickness using the Equation (4) using the remaining differentialwaveform pattern databases 15.

For candidates in the plurality of wavelength ranges, for example, whenthe top 10% variation is excluded, and when the top 20% variation isexcluded, respectively, an instantaneous film thickness Zs at the timepoint s of DBp is calculated, a difference from the film thickness r(m)sis calculated, and the wavelength range having a smaller difference isselected as an optimum wavelength range.

For the coefficients σ in the Equations (5) and (6), a plurality ofcoefficients σ may be set for calculating the instantaneous filmthickness Zs, and combinations of the wavelength range and thecoefficient σ may be processed to specify the combination having a smalldifference. The wavelength range and the coefficient σ specified in suchmanner are stored in the film thickness calculating recipe 17.

In the present embodiment, by using the Equation (6), the film thicknessis calculated by a weighted sum of a plurality of databases having asmall difference from the differential waveform pattern obtained fromthe processing target material 4 in the plurality of databases. Since amore similar differential waveform pattern can be obtained fromprocessing target materials having similar fine shapes, even when thefine shape of the processing target material 4 varies, databases ofprocessing target materials having similar fine shapes can be used, sothat the end point can be determined accurately.

Next, a procedure for calculating the remaining film thickness or theetching amount of the processing target film when the etching processingis performed by the etching amount measuring unit 8 of FIG. 1 will bedescribed using the flowchart of FIG. 6. FIG. 6 is a flowchart showing aflow of an operation for detecting a remaining film thickness etchingamount of the plasma processing apparatus according to the embodimentshown in FIG. 1. FIG. 6 mainly shows a flow of an operation of theetching amount measuring unit 8. A processing starts from step S601.

In the embodiment, a value of a target remaining film thickness of theprocessing target film and a plurality of differential waveform patterndatabases used for detection or determination thereof are set (stepS602) prior to the processing of the processing target material 4.

In the differential waveform pattern databases, interference lightpattern data obtained when the test processing target material havingthe same material, shape, and composition as the processing targetmaterial 4 which is to be processed for manufacturing the semiconductordevice and the film structure on the surface thereof is etched under thesame condition as the processing target material 4 is used as the dataP(m) sj collected for the plurality of processing target materials.

Next, a processing of optimizing the wavelength range and thecoefficient used for calculating the instantaneous film thickness isperformed (step S603). The processing will be described with referenceto a flowchart in FIG. 7 described later. A wavelength range and acoefficient specified in advance may be used without executing theprocessing.

Next, the plasma 3 is formed in the vacuum processing chamber 2, theprocessing on the film to be etched of the material 4 is started, andinterference light obtained from the film to be etched during theetching processing is detected at predetermined sampling intervals (forexample, 0.1 to 0.5 seconds) (step S604). At the time, a sampling startcommand is issued upon the start of the etching processing.

During the processing, an intensity of multi-wavelength interferencelight that changes as the etching progresses is transmitted to thespectroscope 9 of the etching amount measuring unit 8, and is detectedand output by a light detection device thereof as a light detectionsignal having a voltage corresponding to the intensity of light at eachpredetermined frequency.

The light detection signal of the spectroscope 9 is digitally converted,and the sampling signal yij as a data signal associated with anarbitrary time point is acquired. Next, the multi-wavelength outputsignal yij from the spectroscope 9 is smoothed by the first digitalfilter 10 in a first stage, and the time series data Yij at thearbitrary time point is calculated (step S605).

Next, the time series data Yij is transmitted to the differentiator 11,and the time series differential coefficient dij is calculated by thepolynomial adapted smoothing differential method (step S606). That is,the differential coefficient di of the signal waveform is detected bythe polynomial adapted smoothing differential method.

The differential coefficient dij is transmitted to the second digitalfilter 12 in a second stage, and the smoothed differential coefficienttime series data Dij is calculated (step S607). The obtained smootheddifferential coefficient time series data Dij is divided by the smoothedtime series data Yij and transmitted to the individual film thicknesscalculator 13.

Although the smoothed differential coefficient time series data Dij isused here, any value may be used as long as it is time series data thatreflects the difference in the processing target material 4, such as Yijitself, or a value calculated by using a least squares method on Yij.

In the individual film thickness calculator 13, the remaining filmthickness and the interference light pattern data Q (m) sj of theprocessing target film is extracted for each of the plurality of thedifferential waveform pattern databases 15 in the differential waveformpattern database set 14 (step S608).

For example, for each of the above differential waveform patterndatabases 15, data in which s is equal to or longer than a predeterminedelapsed time and remaining film thickness data corresponding to the timeare extracted.

Alternatively, an elapsed time from the start of the etching processingmay be obtained, and data having an elapsed time s within apredetermined range (for example, ±10 seconds) from the elapsed time andremaining film thickness data corresponding to the time may beextracted.

Alternatively, for each of the above differential waveform patterndatabases 15, an elapsed time having the smallest pattern differenceobtained by comparing with the actual pattern Dij of the interferencelight corresponding to the predetermined elapsed time and a remainingfilm thickness at the time may be extracted.

Next, the weighted film thickness calculator 16 calculates a value ofthe instantaneous film thickness value Zi at the time point i by usingthe interference light pattern data Q(m)sj and the remaining filmthickness data r(m)s extracted for each database (step S609).

For the calculation of the instantaneous film thickness value Zi, thematrix Q in which the patterns extracted from each differential waveformpattern database 15 are combined with the data Q(m)sj, and the matrix Rin which the remaining film thicknesses Ru extracted in a similar mannerare combined are created.

The value of the instantaneous film thickness value Zi is calculated bysubstituting Q, R, and the smoothed differential value time series dataDij at the time point into the above Equations (4), (5) and (6). Thewavelength range for summing and the coefficient σ in the Equations (5)and (6) use a predetermined value or a value determined by the flowshown in FIG. 7, which will be described later.

Next, the regression analyzer 18 obtains the first order regression lineusing the calculated instantaneous film thickness value Zi and theinstantaneous film thickness Zi at the sampling time point i stored inthe storage device, and calculates the calculated film thicknessfollowing the first order regression line (step S610).

Further, the current calculated film thickness of the processing targetfilm is compared with the target remaining film thickness set in stepS302, and when it is determined that the thickness is equal to or lessthan the target remaining film thickness, it is determined that thetarget is reached, and a signal for ending the etching processing istransmitted to the plasma processing apparatus 1 (step S611). When it isdetermined that the target is not reached, the processing returns tostep S305. If it is determined that the target is reached, a setting ofa sampling end is finally performed (step S612).

Next, using the flowchart of FIG. 7, a procedure for performing therecipe optimization processing performed by the etching amount measuringunit 8 in FIG. 1 corresponding to S603 in FIG. 6 will be described. Aprocessing starts from step S701.

First, the recipe optimizer 21 determines the remaining film thicknessfor comparing the differential waveform patterns (reference filmthickness). The film thickness may be, for example, a target remainingfilm thickness (step S702).

Next, in each differential waveform pattern database 15, pattern dataP(m)sj of the differential waveform at the reference film thickness isextracted (step S703).

Next, the standard deviation of P(m)sj for each wavelength j iscalculated by using the extracted pattern data P(m)sj (step S704).

Next, wavelengths are relatively excluded in a descending order of thestandard deviation, and the remaining wavelength ranges are used ascandidates for wavelength ranges to be used (step S705). Here, aplurality of candidates are created, such as a case where 10% isexcluded and a case where 20% is excluded.

Next, a plurality of candidates for the coefficient σ in Equations (5)and (6) are created (step S706).

Then, a processing is performed in which one database among thedifferential waveform pattern databases 15 is extracted, theinstantaneous film thickness is calculated using the Equation (4) usingthe remaining differential waveform pattern databases 15, and an errorfrom the remaining film thickness data r(m)s is calculated (step S707).The processing is performed for combinations of the wavelength range andthe coefficient σ so as to specify a combination having a small error.

As described above, the specified wavelength range and the coefficient σare stored in the film thickness calculating recipe 17 (step S708).

Thereafter, the processing is ended (S709).

An effect of the present embodiment will be described with reference toFIG. 8. Here, the differential waveform pattern 710 obtained bydetecting the reflected light from the processing target material 4 andtwo differential waveform pattern databases 15 are taken as examples. Inthe differential waveform pattern 711 of DB4 in FIG. 8, comparing withthe processing target material 4, the processing target film area 213 ofthe test semiconductor wafer (test processing target material) in whichthe differential waveform pattern database 15 is measured is smaller,and the mask film thickness 211 is thicker. In the differential waveformpattern 712 of DB5, comparing with the processing target material 4, theprocessing target film area 213 of the test semiconductor wafer in whichthe differential waveform pattern database 15 is measured is of the samedegree, and the mask film thickness 211 is of the same degree.

In the wavelength range 702 in FIG. 8, a time change of the interferencelight of the processing target film 202 is mainly measured. In thewavelength range 701, not the time change of the interference light ofthe processing target film 202 but a sum of the time change of theinterference light of the mask 201 thinner than the processing targetfilm with the time change of the interference light of the processingtarget film is measured.

Here, a case is considered in which the differential waveform pattern711 of the DB4 and the differential waveform pattern 710 of theprocessing target material 4 are compared, and a film thickness when adifference between the two is small is used in the instantaneous filmthickness calculation. First, in DB4, since the processing target filmarea 213 of the processing target material 4 is small, the time changeof the interference light of the processing target film 202 to bemeasured is small, and an amplitude of the differential waveform patternin the wavelength range 702 is smaller than that of the processingtarget material 4. Therefore, when the differential waveform pattern 711of the DB4 is used, the differential waveform pattern indicating theinterference light of the processing target film 202 does not match, anda calculation accuracy of the difference in the differential waveformpattern is reduced.

This also means that the differential waveform pattern having a smalldifference in the time change (wavelength range 701) of the interferencelight of the mask film thickness 211 is selected, and thus thedifferential waveform pattern 711 in a case where the mask filmthickness 211 is close to the thickness, that is, in the state where theetching is more advanced in DB4 (when the processing target film 202 isthin) is selected, which generates an error in the instantaneous filmthickness calculation.

In such manner, it can be seen that if a differential waveform patterndatabase 15 of a test semiconductor wafer having a different fine shapeon the processing target material 4 is used, a calculation accuracy ofthe remaining film thickness is lowered. On the other hand, in aprocessing target material 4 having a similar fine shape, the differencein the differential waveform pattern becomes small as in thedifferential waveform pattern 712 in DB5.

Therefore, by weighting the differential waveform pattern database 15using the difference in the differential waveform pattern, the filmthickness can be detected with high accuracy by using differentialwaveform pattern databases 15 measured on test semiconductor wafers withsimilar fine shapes in each processing target material 4, even when thefine shape of the processing target material 4 varies.

According to the present embodiment, highly accurate film thicknessestimation and end point determination under various structuralvariations between wafers, lots, and the like can be achieved, and ayield of device manufacturing can be improved.

While the invention made by the inventor has been described in detailbased on the embodiments, the invention is not limited to theabove-described embodiments, and various modifications can be madewithout departing from the scope of the invention. For example, theabove-described embodiments have been described in detail for easyunderstanding of the invention, and the invention is not necessarilylimited to those including all the configurations described above.Further, a part of the configuration of each embodiment may be added,deleted, or replaced with another configuration.

What is claimed is:
 1. A plasma processing method using a plasmaprocessing apparatus that generates plasma in a state where an inside ofa vacuum processing chamber is exhausted to vacuum, so as to process aprocessing target film formed on a processing target material, theplasma processing method comprising: a step of detecting, by a lightemission detection unit at a time instance during a period of processingthe processing target film, light emission of the plasma generatedinside the vacuum processing chamber; a step of obtaining, by acalculation unit, a differential waveform data of a plurality ofwavelengths of the light emission of the plasma detected by the lightemission detection unit; a step of calculating, by a film thicknesscalculation unit, an estimated value of the film thickness of theprocessing target film processed on the processing target material atsaid time instance by weighting each thickness value of the processingtarget film which is indicated by each corresponding pattern in theplurality of differential waveform pattern data stored in a databaseunit in advance based on differences between the differential waveformdata obtained in the time instance by the calculation unit and eachvalue of the plurality of pieces of differential waveform pattern data;and a step of determining, by an end point determination unit, an endpoint of processing using the plasma based on the estimated value of thefilm thickness of the processing target film calculated by the filmthickness calculation.
 2. The plasma processing method according toclaim 1, wherein calculation by the film thickness calculation unit ofthe estimated value of the film thickness of the processing target filmis performed by using a plurality of databases having differentinterference spectrum patterns due to differences in a film thicknessand a structure stored in the database unit.
 3. The plasma processingmethod according to claim 1, wherein said calculation by the filmthickness calculation unit of the estimated value of the film thicknessof the processing target film is performed by using a plurality ofpieces of differential waveform pattern data in a wavelength rangeexcluding pieces of differential waveform pattern data corresponding toa part of said range in which a light intensity has a standard deviationof at least 10% with respect to a predetermined standard deviation,which deviation is a variation in light intensity at each wavelength ofa plurality of pieces of differential waveform pattern datacorresponding to a specified reference film thickness among theplurality of pieces of differential waveform pattern data stored in thedatabase unit.
 4. The plasma processing method according to claim 1,wherein the light emission detection unit detects reflected light oflight projected to the processing target material from a light sourcefor projecting light to the processing target material.
 5. The plasmaprocessing method according to claim 1, wherein calculation of theestimated value of the film thickness of the processing target film isperformed by calculating weight based on the differences between thedifferential waveform data of the light emission of the plasma obtainedby the calculation unit and the pieces of differential waveform patterndata stored in the database unit, and calculating the estimated value ofthe film thickness of the processing target film by using the calculatedweights and the differential waveform pattern data stored in thedatabase unit.
 6. The plasma processing method according to claim 5,wherein when calculating the estimated value of the film thickness ofthe processing target film, as the weight calculating based on thedifferences between the differential waveform data of the light emissionof the plasma obtained by the calculation unit and the pieces ofdifferential waveform pattern data stored in the database unit, the filmthickness calculation unit sets a first value when the differentialwaveform data of the light emission of the plasma obtained by thecalculation unit at a certain time point and the differential waveformpattern data of each database are more similar, and sets a second valuewhich is smaller than said first value when the differential waveformdata and the differential waveform pattern data are less similar.